Attachment D - Stormwater Report · MCU18/0013

      Table 1 - Detention system details

                             Description                                                Value

        Tank Model                                                         20 x Atlantis Flo-Tank - Triple

        Gross Volume (m3)                                                                7.32

        Detention Capacity (m 3)                                                         6.96

        Dimensions (m)                                                      4.08(L) x 1.37(W) x 1.31(H)

        Infiltration Rate (m/d)                                                          0.6

        Catchment Area to Tank (Ha)                                                     0.0420

        Catchment Area Bypassing Tank (Ha)                                              0.0215


       3.3              Hydrologic and Hydraulic Modelling
      The hydraulic and hydrologic modelling software package XPSTORM was used to model the pre-developed
      and post-developed flow conditions for the site. XPSTORM provides a simulation of the natural runoff
      processes and the hydraulic performance of stormwater infrastructure. An integrated 1D/2D hydraulic model
      was developed incorporating the TUFLOW engine. The TUFLOW engine accurately represents site specific
      topography, defining flow paths, discharge, storage, and variation in flow direction in addition to modelling
      flood hazard.
      Hydrologic Modelling

      The 10 year ARI event was defined as the minor storm and the 100 year ARI event was defined at the major
      storm for the analysis. A number of storm durations including the 5 minute, 10 minute, 25 minute, and 1 hour
      duration were simulated for each ARI for the pre developed and post developed model.

      Rainfall data for the 10 minute, 25 minute, and 1 hour durations for each ARI was obtained from the ARR
      2016 data hub. The ensemble of storms for each duration was simulated and the median storm for each
      duration & ARI was determined utilising the ensemble statistics utility. The resultant storms were utilised as
      the design storms for the 10 minute, 25 minute, and 1 hour duration events for each ARI. The ARR 2016 data
      hub does not contain data for the 5 minute duration storm. Data for the 5 minute storm was therefore
      obtained from the IFD generated from the Bureau of Meteorology. Determination of the median event was
      not applicable.
      The Laurenson method was utilised to calculate runoff hydrographs with the following losses:

                Pervious areas – initial and continuing losses of 10mm and 3mm respectively

                Impervious areas – initial and continuing losses of 2mm and 0mm respectively
      Hydraulic Modelling

      An integrated 1D/2D model was developed to simulate the hydraulics of the stormwater drainage network.
      The 1D network was limited to modelling the infiltration/detention tank in the post developed model. Physical
      parameters for the storage node were calculated based on data obtained from the manufacturer.

      The following parameters were utilised in developing the 2D network:

                A 1m grid cell size was utilised.
                The DTM was derived from survey data obtained from CadCon.

                Manning’s roughness for of 0.06 was considered appropriate due to the land use of the site.

                A 2D head boundary line with a free outfall was used to define the 2D model extent.

                                           24 Arakoon Street, Sunshine Beach QLD 4567
Job No – S18-003                              STORMWATER MANAGEMENT REPORT                                       3